The prevalence of hypovitaminosis D in reproductive age African-American women occurs at a rate of >40%. Two factors have contributed to this public health problem: an inadequate DRI for vitamin D and avoidance of sun exposure/use of sunscreen. This startling rate of hypovitaminosis D requires that the DRI for vitamin D in pregnancy be evaluated in a detailed manner. The Cochrane Library (2002) released a report stating that there is insufficient data to evaluate the effects of vitamin D supplementation during pregnancy. Recently, the safety of prolonged supplementation with up to 25x's DRI (10,000 IU/day) was demonstrated in nonpregnant adults. It is essential to determine what dose of vitamin D is required to eliminate hypovitaminosis D during pregnancy and provide the fetus/neonate with adequate vitamin D stores during development and growth, particularly in darkly pigmented individuals. The aim of this research proposal, then, is to determine the efficacy, effectiveness, and safety of maternal vitamin D supplementation (as a function of ethnicity and UV exposure) in the prevention of hypovitaminosis D in the pregnant mother and her fetus/neonate. We hypothesize that darkly pigmented mothers will require substantially higher oral supplementation with vitamin D to eliminate hypovitaminosis D as compared to their Caucasian counterparts. We propose a comprehensive clinical trial to test our hypothesis. Mothers at 12 weeks' gestation will be randomized to one of three vitamin D treatment groups: (1) Control, 400-, (2) 2,000-, or (3) 4,000 IU/day to be continued throughout pregnancy. Calcium and vitamin D homeostasis and skeletal remodeling in mother will be monitored closely throughout pregnancy. Bone density of mother will be measured at 12 weeks' gestation and one-month postpartum. Follow-up growth and skeletal integrity assessments of the infant will be performed at birth, 1, 6 and 12 months stratified by infant feeding regime. Through these proposed studies, the prevalence of hypovitaminosis D among mothers, their developing fetuses and neonates, and the utility of maternal therapeutic intervention with vitamin D for both mother and fetus/infant will be assessed. [unreadable] [unreadable]